Lysine 2,3‐aminomutase: is adenosylmethionine a poor man's adenosylcobalamin?

The interconversion of lysine and β‐lysine, which is catalyzed by lysine 2,3‐aminomutase, is formally similar to the isomerization reactions catalyzed by adenosylcobalamin‐dependent aminomutases. However, lysine 2,3‐aminomutase is activated by 5‐adensoylmethi‐onine and not by adenosylcobalamin. Lysine 2,3‐aminomutase also contains [FeS] clusters, Co(II), and pyridoxal 5′‐phosphate, all of which are required for maximum activity. Lysine 2,3‐aminomutase acts through a mechanism akin to that of the adenosylcobalamin‐dependent enzymes in which substrate radicals are intermediates. However, the 5‐deoxyadenosyl moiety of S ‐adenosylmethionine mediates hydrogen transfer in place of the 5′‐deoxyadenosyl moiety of adenosylcobalamin. 5′‐Deoxyadenosine is an intermediate in adenosylcobalamindependent reactions and in the reaction of lysine 2,3‐aminomutase. The 5′‐deoxyadenosyl radical, derived either from adenosylcobalamin or S ‐adenosylmethionine, appears to participate in these reactions. Similarly, the ribonucleotide reductase from Lactobacillus leichmanii is activated by adenosylcobalamin, whereas the ribonucleotide reductase from anaerobically grown Escherichia coli is activated by S ‐adenosylmethionine and an activating enzyme. The 5′‐deoxyadenosyl radical seems to participate in the activation of both reductases. Therefore, both adenosylcobalamin and 5‐adenosylmethionine appear to serve as sources of 5′‐deoxyadenosyl radicals in nature. S ‐Adenosylmethionine is not as chemically elegant a molecule as adenosylcobalamin, so it may be regarded as “a poor man's adenosylcobalamin.”—Frey, P. A. Lysine 2,3‐aminomutase: is adenosylmethionine a poor man's adenosylcobalamin? FASEB J. 7: 662‐670; 1993.